I have a 1989 Ford F150 4x4 new Jasper 302 installed about 10 years ago drove very little 8-10k sits most of the time new interest in playing with it runs good cold smokes a little after 20-30 min of run time smokes a lot, no power, lifters rattle acts like running on 4 cyl can't figure it out

Have you thought about compression testing each cylinder?

seals or rings are gone somewhere letting oil get into the combustion chamber. It will not be cost effective to fix this issue compared to getting a newer more efficient vehicle.

Not driving a vehicle is definitely not good. A friend in his 70's purchased a new Oldsmobile in 1992. By the time he got around to telling me it wasn't running right it was 2013. When I got into the vehicle to start it I noticed it had 8K miles on the odometer. To make a long story short it started but every seal in the engine was dried up and shot. I suspect the cylinder walls also rusted up thus destroying the rings.